The CAS Registry Mumber 25863-18-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,5,8,6 and 3 respectively; the second part has 2 digits, 1 and 8 respectively. Calculate Digit Verification of CAS Registry Number 25863-18: (7*2)+(6*5)+(5*8)+(4*6)+(3*3)+(2*1)+(1*8)=127 127 % 10 = 7 So 25863-18-7 is a valid CAS Registry Number.